1. Field of the Invention
The present invention relates to a method of manufacturing glass parts for connecting optical fibers, and to glass parts for connecting optical fibers manufactured using the method.
2. Prior Art
Glass parts for connecting optical fibers are used as optical connectors, as optical fiber splices and as optical fiber connection supports of optical devices.
An example of such a glass part for connecting optical fibers is an optical connector having a structure shown in FIG. 1. This optical connector is comprised of a cylindrical glass ferrule 10 having a narrow internal hole 11 along its longitudinal axis. Optical fibers 12 and 13 Are held in the internal hole 11, with their end faces 14 in contact with one another. A matching agent (such as an epoxy adhesive or an ultraviolet-cured resin), not shown, in the figure is filled between the end faces 14. The matching agent acts to match the refractive index between the optical fibers 12 and 13 as well as to bond the optical fibers 12 and 13 together.
The ferrule 10 is manufactured by heating and drawing a mother glass which has a cross-sectional shape approximately similar to that of the ferrule 10 and which possesses a through hole, and then cutting the drawn glass to the desired length.
Moreover, the internal hole 11 of the ferrule 10 is tapered at its open ends 15 and 16 so as to facilitate insertion of the optical fibers 12 and 13 into the internal hole 11. The above-mentioned matching agent or an adhesive is filled into the tapered open ends 15 and 16 and into the gaps between the optical fibers 12 and 13 and the wall of the internal hole 11, this being in order to fix the optical fibers 12 and 13 into the internal hole 11.
Methods for tapering the open ends 15 and 16 include an etching method in which unmasked portions are eroded away using a glass-eroding solution (for example, a hydrogen fluoride solution), a sandblasting method in which cutting is carried out using minute abrasive grains discharged from a fine nozzle at extremely high pressure, and a machining method involving drilling or the like.
However, with the etching method, erosion using the glass-eroding solution is slow, meaning that it is difficult to form a deep taper; moreover, an expensive mask is required, and it is difficult to control the amount of etching. It is thus difficult to make the boundary between the taper and the internal hole 11 into a continuous curved surface quickly and at low cost.
With the sandblasting method, the glass is worn down uniformly in all places, meaning that again it is difficult to make the boundary between the taper and the internal hole 11 into a continuous curved surface. Moreover, there is a tendency for the discharging of the minute abrasive grains to shift off-center, meaning that positioning must be carried out to high accuracy.
With the machining method, the machining takes a long time, there is a tendency for the glass parts to be weakened due to chipping or the formation of tiny cracks, and the boundary between the taper and the internal hole 11 ends up as a discontinuous surface. Moreover, there is a tendency for the machine tool (drill etc.) to shift off-center, meaning that it must be centered to high accuracy.
It is an object of the present invention to provide a method of manufacturing a glass part for connecting optical fibers, which allows insertion of optical fibers into the internal hole of the glass part smoothly, and glass parts for connecting optical fibers manufactured using the method.
To attain the above-mentioned object, the present invention provides a method of manufacturing glass parts for connecting optical fibers, comprising heating predetermined parts of a glass tube having an internal hole while applying pressure into the internal hole, to expand the predetermined parts, thus forming tapered portions.
With the manufacturing method according to the present invention, predetermined parts of a glass tube having an internal hole are heated while applying pressure into the internal hole, thus expanding the predetermined parts and forming tapered portions. As a result, a continuous curved surface can be achieved at the boundary between each tapered portion of each obtained glass part and the internal hole thereof, and the surface can be made smooth where the tapers are formed.
In a preferred embodiment of the present invention, the heating of the glass tube and the application of pressure into the internal hole are carried out while restricting an increase in the outside diameter of the glass tube. For example, the heating of the glass tube and the application of pressure into the internal hole are carried out while the glass tube is placed in a frame. In this way, tapers can be formed with no increase in the outside diameter of each obtained glass part at its tapered portion(s).
In another preferred embodiment of the present invention, the heating of the glass tube and the application of pressure into the internal hole are carried out while drawing the glass tube in a longitudinal axial direction thereof. In this way, the outside diameter of each obtained glass part can be reduced at its tapered portion(s).
The method of manufacuring glass parts for connecting optical fibers according to the present invention further comprises cutting each of the predetermined parts of the glass tube to obtain an open end in which one of the tapered portions is formed, after the heating of the glass tube and the application of pressure into the internal hole.
To attain the above object, the present invention further provides a glass part for connecting optical fibers manufactured as described above, wherein at least one of the open ends of the glass part is tapered in such a manner that a continuous curved surface is formed at the boundary between the at least one of the open ends and the internal hole of the glass part.
With the glass part according to the present invention, the boundary between each tapered portion and the internal hole is a continuous curved surface. As a result, optical fibers can be inserted into the internal hole smoothly.
The above and other objects, features and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.